Musar zu Schemuel II 13:42

THOU shouldst know that he who hates men is hated by them, and when this quality takes firm hold of the soul, it destroys it, because it leads to the hatred of the very food and drink with which man sustains life. Besides, he suffers injury through the hostility of men. When excessive love is expended on other than divine things, it is changed into the most violent hatred. As thou knowest from the expression (II Sam. xiii. 15), "Then Amnon hated her exceedingly." He who loves thee for some reason will turn his back, simultaneously with its disappearance and ending. Thou must not trust in the counsel of the enemy, the "Hater." Thus it is written (Prov. xxvii. 6), "The kisses of an enemy are deceitful." From this quality there branches out fretfulness. Thou knowest how the prevalence of fretfulness has been censured, the blameworthiness which attaches to its use and the repugnance the soul feels therefor.

There are several kinds of hatred. There is one who hates his companion because he harmed him in money matters or struck him, or shamed him, or slandered him. For all of these and similar causes, a person should not hate his companion and be silent about his grievance as it is said in connection with the wicked: "And Absalom did not speak with Amnon either bad or good for Absalom hated Amnon" (II Sam. 13:22). But it is a mitzvah that he let his companion know that he feels he has been wronged and say to him, "Why did you do thus and thus to me?". As it is said: "You shall surely rebuke your neighbor" (Lev. 19:17). And if the offender repents and asks the person who was wronged to forgive him, he must forgive him and the one who forgives should not be cruel it is said: "And Abraham prayed to God" (on behalf of Abimelech who had wronged him) (Gen. 20:17). And even if the offender does not ask him to forgive him, the one offended should not hate him but should conduct himself towards him with love, and in the end it will come to this — that the one in the wrong will correct what he has spoiled.

And it is necessary for you to know that he who hates others — they, too, will hate him, and he who increases hatred in his heart will bring evil upon himself. And where there is love that is not for the sake of Heaven, it can turn into very great hatred, as it is said concerning Amnon: "Then Amnon hatred her with exceeding great hatred for the hatred wherewith he hated her was greater than the love wherewith he had loved her" (II Sam. 13:15).